Ontological paradox

An ontological paradox is a paradox of time travel that questions the existence and creation of information and objects that travel in time. It is very closely related to the predestination paradox and usually occurs at the same time. In simpler terms, an object is brought back in time, and it becomes the object that was initially brought back in time in the first place.
Definition
Because of the possibility of influencing the past while time traveling, one way of explaining why history does not change is by saying that whatever has happened was meant to happen. A time traveler attempting to alter the past in this model, intentionally or not, would only be fulfilling his role in creating history, not changing it. The Novikov self-consistency principle proposes that contradictory causal loops cannot form, but that consistent ones can. This theory, however, only makes sense if you're dealing with a wormhole or some other form of time travel where you end up in the same universe as you started. With actual time replication, which is what much of fiction calls "time travel," this could not be the case.
However, a scenario can occur where items or information are passed from the future to the past, which then become the same items or information that are subsequently passed back. This not only creates a loop, but a situation where these items have no discernible origin. Physical items are even more problematic than pieces of information, since they should ordinarily age and increase in entropy according to the Second law of thermodynamics. But if they age by any nonzero amount at each cycle, they cannot be the same item to be sent back in time, creating a contradiction.
Another problem is the "reverse grandfather paradox", where whatever is sent to the past allows the time travel in the first place (such as saving your past self's life, or sending vital information about the time travel mechanism).
The paradox raises the ontological questions of where, when and by whom the items were created or the information derived. Time loop logic operates on similar principles, sending the solutions to computation problems back in time to be checked for correctness without ever being computed "originally."
It is sometimes called the bootstrap paradox, in reference to the expression "pulling yourself up by your bootstraps"; the term was popularized by Robert A. Heinlein's story By His Bootstraps (see below).
Examples
Involving information
* On his 30th birthday, a man who wishes to build a time machine is visited by a future version of himself. This future self explains to him that he should not worry about designing the time machine, as he has done it in the future. The man receives the schematics from his future self and starts building the time machine. Time passes until he finally completes the time machine. He then uses it to travel back in time to his 30th birthday, where he gives the schematics to his past self, closing the loop. Of course, the schematics must have come from somewhere.
* A professor travels forward in time, and reads in a physics journal about a new equation that was recently derived. He travels back to his own time, and relates it to one of his students who writes it up, and the article is published in the same journal which the professor reads in the future.
* A man builds a time machine. He goes into the future and steals a valuable gadget. He then returns and produces his "invention" to the world, claiming it as his own. Eventually, a copy of the device ends up being the item the man originally steals. This of course means that the "real" device is the copy of it, leaving the loop sealed. However, nobody could have created an original device. And it means the invention was his.
* A young physicist receives an old, disintegrating notebook containing information about future events sent by his future self via a time machine; he copies it over into a new notebook before it deteriorates so badly as to be unusable. Over the years the predictions of the notebook come true, allowing him to become wealthy enough to fund his own research, which results in the development of a time machine, which he uses to send the now old, tattered, disintegrating notebook back to his former self. The notebook is not a paradox (it has an end and a beginning; the beginning where he receives it and the end where he threw it out after he copied the information), but the information is; it is impossible to state where it came from. The professor has transferred the information that he wrote himself, so there was no original notebook.
Involving physical items
* A man is locked outside his house because he's lost his keys. Another man approaches him with the keys. When the man enters his house five minutes later, he encounters a time machine which transports him and his keys back in time five minutes, allowing him to give them to himself and close the loop.
Examples from fiction
Literature
* Robert A. Heinlein's stories "By His Bootstraps" and "—All You Zombies—" involve the predestination paradox, but also play with the ontological paradox. In "By His Bootstraps", the protagonist is asked to go through a time portal by a mysterious stranger, a second stranger tries to stop him, and all three get into a fight which results in the protagonist being pushed through anyway. Ultimately, it is revealed that all three are the same person: the first visitor is his future self and the second an even older future self trying to prevent the loop from occurring. The ontological paradox here is in where and how the loop started in the first place. "—All You Zombies—" involves an even more convoluted time loop involving kidnapping, seduction, child abandonment and sex reassignment surgery, resulting in the protagonist creating the circumstances where he becomes his own mother, father, son, daughter, forever-lost lover and kidnapper.
* In Jasper Fforde's novel The Eyre Affair, a time-traveling character goes to Elizabethan times to discover . After discovering that neither Shakespeare, Marlowe, Bacon nor anyone else seems to have written them, the character must give Shakespeare a copy of his own Complete Works and a rough timeline to ensure their existence in the future. (Confusing things further, however, the sequel revealed that the plays given to Shakespeare only included three comedies. The characters speculate that they proved so popular he wrote new ones himself. Fforde rather makes a point of not having his time travel follow any particular set of rules.)
* In Harry Harrison's novel The Technicolor Time Machine, Barney Hendrickson travels back in time to present his earlier self with a note explaining how to resolve a seemingly insurmountable difficulty. The younger Barney carefully folds the note and puts it in his wallet, expressing his intention to leave it there until he reaches the point in his life where he travels back in time to hand it to his younger self. This prompts some discussion of how the note actually got written, and by whom, which the older Hendrickson dismisses by saying that the note was written by "time" because it needed to exist to allow the predestination paradox to play out. At the close of the novel, Hendrickson also discovers that by traveling back in time to film the Viking settling of America, he actually caused it to occur.
* In Terry Pratchett's novel Pyramids, the immortal High Priest Dios has been advising a line of kings for thousands of years. At the end of the book, Dios falls backwards in time where he becomes adviser to the first king of the line. His life is thus a closed loop.
* In The Green Futures of Tycho, the protagonist discovers a time travel device but is unaware of how to use it, and ends up simply traveling to random times. He eventually meets an older version of himself who explains the controls on the device and how to use it properly to get to exact dates. However it is never explained how this information was initially learned; one can only assume his older self knows how to use the device from remembering the event earlier.
* In Tim Powers' The Anubis Gates, Brendan Doyle is a twentieth century English scholar studying the work of early nineteenth century poet William Ashbless whose most famous poem is called "the 12th hours of the night". Doyle goes back to nineteenth century England and hoping to meet Ashbless, he goes to the pub where Ashbless wrote "the 12th hours of the night" on the night where Ashbless allegedly wrote the poem. Ashbless does not show up and out of frustration, Doyle writes on a piece of paper the text of "the 12th hours" that he knows by heart. It is later revealed that he is Richard Ashbless. Hence, nobody wrote "the 12th hours of the night", nor any of Ashbless' works, since Doyle merely transcribed it from memory.
*In Audrey Niffenegger's novel The Time Traveler's Wife, the protagonist, Henry DeTamble, time travels involuntarily. After he marries, he begins to frequently travel to various times in his wife's childhood, during which he befriends her, which leads to their eventual marriage. Shortly after his wife's younger self first meets him, he dictates to her a list of the dates on which he will reappear; when she eventually meets his present self (who has not yet traveled into the past to meet her), she gives him the same list of dates, which he memorizes so that he can dictate it to her when he travels into the past. Neither character can figure out how or where the list originated.
*In Mark Anthony's The Last Rune series, the protagonist is given a pair of magic spectacles by a friend of his. Later on, he travels back in time and ultimately returns the spectacles to his friend, a hundred and fifty years before he received them.
* In Peter F. Hamilton's Fallen Dragon, the quasi-sentient software Prime is able to decrypt the best-available encryption of the time, enabling the rebellion on Thallspring. Lawrence has had a copy of Prime since his teens somehow; he got it from his mysterious friend Vinnie, who ultimately turns out to be time-travelling Lawrence himself, from the future.
* In the comic book Next Men by John Byrne the main villain is a US Senator August Hilltop who, along with a cyborg named Sathanas who was recovered from a crash site, is attempting to create superhumans. In a prequel to the series, called 2112, it is revealed that Sathanas is a superhuman from a future where his and Hilltop's project was successful. Thus his travelling back in time introduces the necessary knowledge to create the future he comes from. It is also strongly implied in the series that Sathanas is actually Senator Hilltop from the future.
* In 2009, Marvel Comics published The Marvels Project, a miniseries intended as an origin story of the concept of superheroes within the Marvel Universe. The series identifies Dr Thomas Holloway as the first person to become a "super hero" in that he dons a costume, assumes a new identity and fights crime. In the mini series Holloway is inspired to do so in part by the tales of an elderly patient of his. This patient turns out to be the Two Gun Kid who shared a number of time travelling adventures with superheroes from the present. Thus, the idea for the superhero ultimately comes from a future where superheroes are well established.
Film
*In the movie Back to the Future, Marty McFly performs the song "Johnny B. Goode" at a high school dance in 1955, after the band's guitarist (who happens to be named Marvin Berry) injures his hand. Astounded by McFly's rather prescient guitar heroics (which include imitations of the future Pete Townshend and Eddie Van Halen), Marvin calls his cousin Chuck Berry, who listens in on "the new sound been looking for". This creates an apparent paradox, with the song "Johnny B. Goode" having never actually been written by anyone.
* In the film Bill And Ted's Excellent Adventure the protagonists, Bill S. Preston Esq. and Ted "Theodore" Logan, are met by Rufus, a figure from the future who gives them access to a time machine. To convince them he is telling the truth, older versions of Bill and Ted appear in the time machine and tell them, "Listen to this dude Rufus; he knows what he's talking about." Rufus himself never tells them his name. Ontological paradoxes are frequently used in other parts of the movie and its sequel, Bill & Ted's Bogus Journey.
* In the film Ink, the titular character, Ink, kidnaps a little girl, Emma, presumably setting in motion one possible sequence of events that lead to his own creation. The death of Emma (as a result of being kidnapped and sacrificed) causes her father, John to commit suicide: he becomes Ink and is tasked with abducting his former daughter. The paradox is resolved when other characters alter the timeline, and allow Ink to rescue Emma from sacrifice, thus ensuring that he will no longer exist.
* In the film Somewhere in Time based on the Richard Matheson novel Bid Time Return, Christopher Reeve's character is given a pocket watch by an old lady. He then goes back in time and gives the pocket watch to the old lady's younger self, played by Jane Seymour, which prompts her to seek him out years in the future and give him the watch, resulting in the watch having no apparent origin.
* In the Futurama film Bender's Big Score, the tattoo of Bender on Fry's backside, which contains the time code, is put there by Bender who took it off future Fry's backside. The question of how the tattoo was created creates an ontological paradox.
* In Star Trek IV: The Voyage Home:
** In the twentieth century, Scotty and McCoy purchase supplies from a plastics-manufacturing plant; as payment, they offer their host, a Dr. Nichols, the formula for transparent aluminum. McCoy pulls Scotty aside and says, "If we give him the formula, we're altering history", to which Scotty replies, "Why? How do we know he didn't invent the thing?" In the novelization of the film, it is explicitly revealed that Dr. Nichols did invent transparent aluminum.
** In twentieth-century San Francisco, Kirk pawns an antique pair of glasses to raise money. These glasses were originally given to him as a gift in the 23rd century by Dr. McCoy, who says they are 400 years old. The retconned implication is that McCoy acquired the glasses that Kirk left in the past.
* In Timerider: The Adventure of Lyle Swann, the eponymous character travels from present-day America to 1877 Baja California and encounters a woman named Claire Cygne. During the course of the story he tells her of his life in Los Angeles, California. They have sex, and he eventually returns to his own time. Just before that return, Claire takes a metal pendant from Swann that he had previously told her had been passed down to him through the generations, beginning with his great-great-grandfather having given it to his great-great-grandmother—after which his great-great-grandfather mysteriously disappeared from her life. Swann's great-great-grandmother then went to Los Angeles to try to find his great-great-grandfather, settled there, and became the matriarch of the Swann family. The implication of these events is that Swann has become his own great-great-grandfather via the presumption that Claire had become pregnant with her own great-great-grandson's child, Anglicized her name to Swann, then went to Los Angeles in a vain attempt to find Swann himself. The pendant itself and the information Swann passed on to Claire, as well as his own semen, become paradoxical.
* In The Terminator movies:
** The Terminator cyborg sent back in time to kill Sarah Connor is destroyed, but its components are salvaged to form the basis of the artificially intelligent computer network Skynet that will, in the future, send it back in time on its murderous mission. The knowledge of how to create an artificially intelligent machine therefore has no ultimate source.
** While in the past, Kyle Reese- the soldier sent from the future to protect Sarah so that she can give birth to his future commander John Connor- falls in love with Sarah and has sex with her, resulting in him becoming the father of his own commander. In essence, John Connor and Skynet both exist as a result of the same ontological paradox, as the means by which they could come into existence in the past came from a future where they had already been created.
** Kyle gives Sarah a message from the future John. In Terminator 2: Judgment Day, young John says that his mother made him memorize the message — which, ironically, says that the future can be changed — in order to give it to his father, so that his father might then pass it on to her. At no point do we learn when or how the message was originally composed. Similarly, Kyle shows Sarah how to fight Terminators. Sarah teaches the same methods to John, who trains Kyle in the future. Also, Sarah Connor knows that her unborn son is called John Connor because Kyle Reese said so - the character's name is in and of itself an ontological paradox.
** In the movie Terminator 3: Rise of the Machines, the Terminator tells John Connor and Katherine Brewster that he was sent by Katherine herself after she reprogrammed him to serve the Tech Comm resistance. Later in the movie, he takes the couple to Sarah Connor's grave and tells them that Sarah buried her weapons there. Since Katherine knew about the weapons location because the Terminator told her, then she told this same information to the Terminator before sending him to the past, the origin of the information about the weapons location remains a complete mystery (Although, since the Terminator mentions that it was put in there in accordance to Sarah Conner's Will, it is possible that John learned about the weapons later and the Terminator's presence simply meant that he recovered the stash earlier).
Television
* In similar scenes in both episode 2.6 of Life on Mars and "Allison from Palmdale" of Terminator: The Sarah Connor Chronicles, the pregnant mothers of Sam Tyler's future girlfriend, Maya Roy, and Cameron Phillips' future flesh pattern, Allison Young each decide upon her daughter's name following a conversation with Sam or Cameron, respectively, in which the time traveller mentions the name. The unborn fetus thus provides her own name to herself through Sam or Cameron, and it is never originally created. Sydney Fields similarly names herself through time-traveler Derek Reese. In the Terminator: The Sarah Connor Chronicles episode, "Alpine Fields"; unlike the other two examples in which the pregnant mothers are unaware of the time-traveler's knowledge of the future, Sydney's natural mother and half-sister/adoptive mother know who Derek is and what Sydney will do in the future.
* In the beginning of the Dexter's Laboratory made-for-TV movie , a group of robots who came from the future from Dexter's time machine tell him they are there to "destroy the one who saved the future". After he easily destroys them all he goes into the future to see how he saved the future. In the end of the film during the showdown against his arch-enemy Mandark, Dee Dee saves the world by wandering in from the open time gate and pressing the button to reverse the waves of the "Neurotomic Protocore", thus turning the dystopian world into a utopian world. The four Dexters, overcome with rage, create a group of robots and tell them to "destroy the one who saved the future", and send them back through the time machine to take care of Dee Dee, creating an ontological paradox. When Dexter notices that this paradox is too confusing, he decides to ignore it and goes to eat lunch.
* In the Star Trek: Deep Space Nine episode Visionary, is sent forward in time periodically, seeing himself die several times. He tries to stop events by telling Quark to not allow any Klingons into his Bar, but Quark does so anyway because of his greed for the Klingons' money. When the reason for his time travel (radiation intensified by a singularity) is discovered, O'Brien travels forward in time once more and finds Deep Space Nine being evacuated, his future self telling him there was an explosion. When he returns to his own time, armed with the knowledge, he is forced to have the radiation intensified, which sends him into the future. He tells his future self the station will be destroyed, and they head to Operations, seeing the cause of the attack: a Romulan Warbird in orbit around the station, its cloaking device powered by a singularity, the explosion occurring after the Warbird decloaks and attacks. O'Brien is too weak to return, the radiation killing him, and he gives the device which allowed his future travel to his self, who returns and reveals the events. In comical and ontological fashion, he finds himself having experienced a day or so before everyone else, and feels that "somehow this was the other O'Brien's life". Quark proposes a business deal in which O'Brien would reveal the results of the gambling games he saw; O'Brien refuses, but as he walks out of the bar, he tells Quark "Dabo" just as one is achieved in a game of Dabo at the bar. The episode is unusual because of the number of loops created by the events, and their effect on the history of the show.
* In Red Dwarf:
** In the 1988 episode "Stasis Leak", Rimmer encounters the future holographic version of himself who tells him that the future crew had traveled back in time through a stasis leak found on one of the lower levels of the ship. He writes this in his diary. In the future, Lister reads Rimmer's diary and looks for the leak, which the crew finds and uses to travel back in time, where future Rimmer tells past Rimmer about the leak. The paradox not only involves the knowledge of the leak, but also the fact that the phenomenon itself is called a "stasis leak".
** In the 1997 episode "Ouroboros", Lister meets Kochanski from an alternate dimension who wishes to bear children, so she asks Lister to fill the in vitro canister with his sperm. Later, he notices the label "Ouroboros" on a supply box and recognizes it as what was written on the box in which he was found when he was baby. This makes him realize that he is his own father and Kochanski is his mother, so when the baby is born, he travels back in time, leaving his younger self there in a box and writing "Ouroboros" on it. The paradox is that Lister is his own father, so he caused his own existence. This paradox was, however, deliberate as the idea was that Lister was meant to be god and his existence in the universe had to be neverending so the human race could never die out.
* In the animated TV series Gargoyles
** The wealth of billionaire David Xanatos is based on an ontological paradox. On his twenty-first birthday, Xanatos receives a letter containing an ancient coin, which is the seed of his entire fortune. Many years later, he follows the instructions in the letter: he travels back in time a thousand years, acquires a small coin, and makes arrangements for it to be delivered to his past self a millennium later. While the letter itself is not an ontological paradox, the written text of the letter, and the information it contains, is.
** An archmage the heroes battled in the past was thrown into a gorge and presumed dead. However, it is later revealed that the archmage's future self appeared, and saved his past self from falling to his death. He then took his past self on a time-travel, sharing various bits of information with him, finding magical artefacts that will give his past self power (confusing the people around him, as he asks for the trinket "The Eye of Odin", which he is already wearing on his helmet), till eventually they arrive in the present (some 1000 years after the archmage fought the Gargoyles). The past version of the archmage then leaves, and travels back into the past to save his past self's life and close the circle.
* In the Futurama episode Roswell That Ends Well, Fry, Leela, Bender, The Professor and Dr Zoidberg are transported to the past, where Fry inadvertently impregnates his grandmother, thus becoming his own grandfather. This is further complicated by the events of The Why of Fry, which reveals that Fry is in the future because of the events of Roswell That Ends Well, and the events of the former episode meant he could defeat the Brains in The Day the Earth Stood Stupid, although (if the episodes are taken to be in a chronological order) this is because of events in the later episode Roswell That Ends Well. In The Why of Fry, the loop is revealed, and complicated by Fry who, armed with knowledge from the future, sends his past self into the future; it is not a pre-destination paradox, as the inconspicuous shadow of Nibbler from Space Pilot 3000 is now joined by Fry's shadow. He breaks the loop by telling Nibbler of the inadequacy of the vehicle he used in the events of The Why of Fry, and this was how he was able to escape the loop with the superior vehicle not forcing him back into the loop.
* In Quantum Leap:
** The time traveler Sam Beckett performs the Heimlich Maneuver on a choking man who is addressed as Dr Heimlich; no one else present recognizes the technique as it had not yet been invented.
** Sam gets a TV host, Captain Galaxy, to share his theories of time travel to a young Sam watching the program, which in turn greatly influences Sam in his own theories of time travel.
** Sam inspires the writing of the song Peggy Sue when in one episode he leaps into a veterinarian whose assistant is Buddy Holly. He points Holly in the right direction after having tentatively come up with "piggy suey", which is what Sam had just called out to a pet pig he had named "Piggy".
* In Doctor Who:
** The 2007 episode "The Shakespeare Code", set in 1599, has a running joke where the Doctor, in the presence of William Shakespeare, quotes lines from plays that Shakespeare has not yet written. In each instance, Shakespeare comments that he "likes that" and might use the line in a future work. The true origin of these lines form an ontological paradox (with the exception of the word "Sycorax", which the Doctor did not use as an intentional reference to Shakespeare, but to an alien species that appeared in "The Christmas Invasion").
** In the 2007 episode "Blink", the Doctor records a message on film in 1969 in the form of half a conversation. The other half is filled in when Sally Sparrow views the film on DVD in 2007, which her friend Lawrence Nightingale transcribes. The full transcript, including the Doctor's portion, is eventually handed to the Doctor in 2008, but before he is sent back to 1969 from his subjective viewpoint, so he can use it in creating the message later. The contents of the conversation form an ontological paradox.
** In the Children in Need mini-episode "Time Crash", the Tenth Doctor meets the Fifth Doctor which causes an extremely powerful paradox strong enough to tear a hole the size of Belgium in the fabric of space and time. The Tenth Doctor saves the day by firing an artificially created supernova into a black hole caused by the paradox thus cancelling out the implosion of the black hole. The Tenth Doctor knows how to do this because he remembers seeing himself do this when he was still the Fifth Doctor.
** In the two-part episode Silence in the Library/Forest of the Dead, Professor River Song tells the Doctor about how in his future, he could open the doors of the TARDIS by simply clicking his fingers, which he dismisses as impossible. At the end of the episode he does open the doors exactly as she described, allowing him to show this River in his future, her past. In addition to this, the Doctor finds that he has stored River Song's consciousness in his future sonic screwdriver after her death, which eventually inspires him to do just that.
** In the 2010 season finale The Big Bang, the Doctor jumps through time all throughout the episode in order to ultimately restore the universe. In each instance, someone shows up in the right time and place because of a message left by the Doctor, who proceeds to go back in time to leave the message that summoned them to the right place and time. Interestingly, the Doctor specifically avoids a physical item ontological paradox twice, once when leaving his sonic screwdriver with Rory 2,000 years in the past, and the next when leaving a note for Amelia on a museum brochure the night before.
* In the Stargate SG-1 episode "1969", SG-1 accidentally travels back in time to the year 1969, where they are aided by Lt. Hammond because of a note his future self gave to Carter before they left, spurred by a familiar cut on Carter's hand. Recalling the memory of the future SG-1 visiting him early in his career, Gen. Hammond had ordered research into using the Stargate for time-travel and was subsequently able to provide them with the information they needed to get home — before they left.
* In Heroes
** In the episode "Out of Time", Hiro Nakamura spreads the stories of 'Takezo Kensei' in the past, only to learn them as a young boy and eventually go back in time to spread them again in the first place.
** In the episode "Our Father", Claire Bennet refers to her past self (a baby) with the nickname "Claire-Bear" to her adoptive father Noah Bennet in the past (who is unaware he is talking to the future Claire), thereby putting the name in his head for him to use - which he has done throughout previous seasons.
* In the TV show Mr. Meaty a new game system comes out and Josh & Parker are first in line, but their brothers cut in front of them. So they decide to go forward in time to when the game system is cheaper. When they get there, they discover that the world is controlled by baboons. Eventually they become the alphamales and go back in time with the baboons. When the baboons are brought back, they realize that the baboons will eventually take over the world.
* In the two-part episode "War Without End" of the TV show Babylon 5, two characters (Jeffrey Sinclair and Zathras) take the space-station Babylon 4 back in time 1000 years, to be used by the Minbari in their war against the Shadows. During the trip back Sinclair transforms into Valen, a Minbari holy leader long known to be "Minbari not born of Minbari", who was roughly equivalent in status to Gautama Buddha, Christ or Mohammed. The paradox is contained in three letters written by Valen for Sinclair, Delenn and Draal; these letters were sealed in a sanctuary on Minbar, with orders that the sanctuary be opened on specific dates and times and the letters then given to the appropriate persons. These letters contained the information about how to send Babylon 4 back in time, as well as identifying Sinclair as the historical Valen. In addition to the letters, the Minbari's religious and historical texts, as well as much of their culture, political structures and religious beliefs, are also an integral part of the paradox. Sinclair had studied these at length before he learned he was Valen, and so when he went back into the past he intentionally created the Minbari history he remembered from the future. There is also a predestination paradox here: Delenn is a human-Minbari hybrid, having transformed at the beginning of season two, however to change she needed human DNA - which the Minbari gained through Valen, himself still partly human. Had Sinclair not gone back, Delenn could not have undergone the transformation - in fact she would not even have been born.
* In the anime series The Melancholy of Haruhi Suzumiya, the time-traveling character Mikuru Asahina comes from the future to observe the reality-bending Haruhi Suzumiya. At one point in the series, an older version of Mikuru comes to the past to pass some important information to Kyon. The older Mikuru went to great lengths to ensure that her younger self did not discover her presence, but, despite all these precautions, she accidentally let slip a small bit regarding the star-shaped mole on her breast. Mikuru herself was not aware of the mole until Kyon had pointed it out to her. However, Kyon himself was not aware of the mole until the older Mikuru pointed it out to him. Although from the dialog of 'future Mikuru', it can be inferred that she and Kyon have a rather intimate future relationship, especially in her warning to Kyon that he should not become too close with her past self, in the future. Ostensibly, because their future relationship creates adverse reactions from Haruhi's influence or "powers" on the immediate future, as is the plot of the series.
** In the second season of the series, Mikuru takes Kyon to the same day and month three years ago. There Kyon meets Mikuru's future self after past Mikuru has been rendered unconscious. After a brief conversation future Mikuru leaves, and Kyon is stuck in the past until past Mikuru wakes up. Kyon decides to sneak into Haruhi's old school with the unconscious Mikuru on his back. There he meets an adolescent Haruhi Suzumiya who blackmails him into helping her write the symbols on the baseball field with a powdered chalk dispenser. Kyon becomes the one who actually drew the symbols on the field that Haruhi became famous for doing when she was in middle school.
* In the 2008 television miniseries The Andromeda Strain, the aforementioned disease is sent back in time via a wormhole by the citizens of future Earth, who cannot stop the disease because a required bacterium has gone extinct and only exists in the past. Scientists in the past manage to utilize this bacteria and kill the virus, but a single sample is saved and stored in the International Space Station at the series' end. It is implied that this sample is the cause of the viral outbreak on the future Earth.
* In the episode "Lost and Founded" of the TV series Aladdin, Iago brings the blueprints for Agrabah almost 700 years into the past and gives them to Jasmine's ancestor, Hamed, who founded Agrabah using them. We never learn how or when the blueprints were originally drawn up. Another paradox involves the origin of Agrabah's name, which Hamed learned from Genie (who was describing Agrabah to him like a real estate agent would describe a neighborhood to a prospective homeowner).
* In British television play The Flipside of Dominick Hide, a time traveller from Earth's future, who illegally visits the London of 1980 to search for an ancestor, falls in love with a local woman. He gets her pregnant, and discovers that he was/is the ancestor he was looking for. It is explained that the character is a victim of something called a "genetic time-slip".
* In the Supernatural episode "In The Beginning" Dean Winchester is sent back in time and meets his mother, and learns that he may be able to kill the Yellow-Eyed Demon, preventing him from killing Mary Winchester, but unwittingly puts the Demon on Mary's scent, allowing him to kill her as shown in the Pilot. It was later revealed by Castiel, however, that the future could not be changed and events would have unfolded the same way had Dean not interfered. In the same episode, Dean stops his father on the way to buying a VW Camper and convinces him to instead buy a Chevrolet Impala, which is a staple of the show and later becomes Dean's.
* In the Family Guy episode "Meet the Quagmires", Peter travels back in time to his senior year of high school. At the prom, Brian sings Rick Astley's hit 1987 single "Never Gonna Give You Up", creating an ontological paradox as it serves as Astley's actual inspiration for the tune. This parodies the "Johnny B. Goode" paradox from Back to the Future as described above.
* In Goodnight Sweetheart, Gary regularly plagiarizes modern day pop songs, introducing them to his 1940s audience.
*In Lost:
**In 5th season, Richard Alpert in 2007 gives John Locke a compass, asking John to give it to him when they next meet. In 1954, John Locke gives Richard the compass. This compass is held by Alpert until 2007, where it is returned to Locke to complete the loop. The compass has no origin.
**In the 4th season episode "The Constant, while consciousness is jumping back and forth between 1996 and 2004, Daniel Faraday tells Desmond in 2004 that he must go and visit Faraday in 1996 and provide him with the settings to make his time travel machine work correctly. Since Lost implies that the major events of history are set and cannot be changed by time travel, this creates an ontological paradox because the 1996 Faraday was given the information for the machine by Desmond, who was given that information by Faraday in 2004.
* In The Two Worlds of Jenny Logan, the antique dress is an example of an ontological paradox.
* In the TV series, Mirror, Mirror, the mirror is an example of an ontological paradox.
* In Terminator: The Sarah Connor Chronicles, Catherine Weaver, a cyborg T-1001, is creating a machine in her company called John Henry which has a lot of similarities to Skynet. In the future, Skynet created the T-1001. The series was cancelled before this plot point was fully resolved, but for a time it seemed possible that Weaver was creating Skynet, which would later create Weaver and send her back in time. That interpretation of events would be an ontological paradox.
* In the children TV series, Johnny Test, in the episode "Old School Johnny", Johnny goes back in time to 1845, when events he will be questioned upon in his present day tomorrow (one day after the time he originally went back in time) on a test in school. However, Johnny changes what happened in those events, therefore changing history. When he returns to his present time, the next day he takes te test, and gets an F because the answers to the test changed because of his own actions.
* In the episode Far From Home in the TV show Justice League Unlimited, Braniac 5 and Bouncing Boy of the Legion of Superheroes in the 30th Century used their time bubble to take three random heroes from the legendary Justice League, to eventually help them beat the Fatal Five, who have captured all their teammates and used mind-control on them. Braniac 5 came up with this idea because according to his research, three heroes from the Justice League DID come to the future, but Bouncing Boy reminds him that three heroes came to the future, but only two made it back home. They then get John Stewart, Green Arrow, and Supergirl, who have been sparring against Zeta robots. Bouncing Boy tells Braniac 5 that the date that he took them was the exact date in which Supergirl disappeared from the historical records, so they both thought that in a battle against the Fatal Five, Supergirl will get killed. It turns out that in the ultimate fight against the Fatal Five, Supergirl survives and the reason why she disappeared from historical records is that she decided to stay in the future, because she fell in love with Braniac 5.
Video games
* In the computer game Escape from Monkey Island, Guybrush Threepwood travels through a marsh where time flows differently and encounters his future self on the other side of a gate, who gives him the gate's key and several other items. Unconvinced, the present Guybrush asks what number he's thinking of, and opens the gate when his future self gives the correct answer. Later in the marsh, Guybrush must go through the gate from the other side, and so has to give his past self the key and the miscellaneous items, then pass the number-guessing test by recalling what his future self told him. The question of where the key and items originally came from is thus never resolved. True to the game's humor, failure to repeat everything precisely will cause a "temporal anomaly" that sends Threepwood back to the start.
*In the game Time Hollow, the hero Ethan receives the pen that will enable him to modify a part of the future. At the end of the game, he opens a time hole to send to his past-self the pen.
*In the MMORPG RuneScape a player may choose to do a quest where they enter the past and aid the first family to come to the game's world. After the quest's conclusion, the player may return to speak to the characters and in one conversation inadvertently suggests the name of the skill that the character founds. Upon realizing this, the player's character tries to name the skill after themselves but the founder has already settled on the first name.
* In the interactive fiction game Sorcerer, the player is given the combination to a safe by his future self. He then has to give the combination to his past self to prevent a temporal paradox.
* In the interactive fiction game Trinity, the player acquires an umbrella from an old lady in the present that he later gives to a young girl in the past (who of course grows up to become the old lady), creating an ontological paradox. Acquiring this umbrella for a second time triggers the epilogue of the game, which implies an infinite time loop for the player.
* In The Legend of Zelda: Ocarina of Time, the protagonist Link learns the Song of Storms from a man found in the future windmill. The player then travels back to the past as a child and plays the song in the windmill as part of the game progression, which is when the teacher first hears it. The song itself is the subject of the ontological paradox.
* The game TimeSplitters: Future Perfect makes frequent use of this paradox. Incidents include the player receiving a key from his future self and handing it later on to his past self (with no clear origin of the key), learning a password in the same manner and on more than one occasion saving his own life (which often entails playing through the same section of the game more than once).
* In Jak II, the protagonists accidentally use a Rift Rider to travel centuries into the future. During the course of the story, one of them, Keira, builds another Rift Rider based on the first one (which gets destroyed after the time travel). At the end of the game, they are forced to send younger versions of Jak and Samos into the past so that they can become old enough to play their parts in defeating Baron Praxis and the Metal Heads, which means the Rift Rider Keira builds is evidently the same Rift Rider she based it on. Further more, the younger version of Jak, whose name was originally Mar, takes the name of his older version for himself, causing the name Jak to have no origin.
* In Jak 3, Jak discovers pieces of armour that were once used by the ancient hero Mar. Near the end of the game, Jak discovers that Mar is actually an older version of himself, who went far into the past, and apparently spread the armour throughout the world. This causes the paradox that the armour was never actually made, and is of infinite age.
* The computer game series Sam & Max Season Two uses this paradox frequently. One instance is when the main characters look out their window and an unknown person calls out to them to ask if he can have the item they are holding. After they give it to him, he gives them an egg in return. They use the egg to later solve a puzzle. In a later episode, the main characters yell at their office window and ask their past selves for the item they are holding, which you use to solve a puzzle. In return you give them the egg that helps them solve the puzzle in the past. Thus revealing that they were the people that helped them in the past and also creating a paradox. The paradox is joked about in normal Sam & Max fashion when, after receiving the egg Sam comments, "Thanks. Be you later." A scene in the second to last episode creates a paradox when the main characters go back in time to Episode 2 of Season 1. Their doubles from that episode then steal the time machine and come into the present time. The main characters reappear in the present, angry at their past selves for having to relive the last two years over. Afterward, the main characters trick their past selves into going back to their original time and trap them there by recalling the time machine. This means that two sets of Sam and Max lived through those two years to get to the current time. This plot hole is written off by a computer who declares "Time stream repaired".
* In Final Fantasy I, Garland's pact with the four fiends sends him into the past where he can re-activate them in the future to send him back again, creating a loop. At the conclusion of the game, the player breaks the loop by defeating Garland.
* In Space Quest 4, Roger Wilco travels in time to different periods and, after his son saves his life in the future, he eventually learns about his wife, Beatrice. This event shapes the events in Space Quest 5 such that if Beatrice dies in any way, Roger Wilco will no longer exist since his son rescued him in the future, and thus he would have died in the future and not existed. But, since Roger Wilco does exist, Beatrice therefore cannot die. The loop basically occurs when Roger Wilco travels into the future, and thus, it is almost predestined that Roger Wilco must know and tell his son to rescue him when the time comes.
* In Timequest, the key to the final puzzle is to cause events as one witnesses them. The game teases players with a nonspecific doomsday machine that can't not be disabled.
* In Dragon Quest V, the hero possesses a magical golden orb. In his childhood, the hero is visited by his future adult self, who, unbeknowenst to the child hero, switches the magical orb with an ordinary gold bauble. Later in his childhood, the hero is enslaved by an evil priest, and the bauble (which is still believed to be the magic orb) is destroyed. In his adulthood, the hero realizes he needs the magic orb to vanquish the demon lord, so he visits a faerie queen who sends him back in time with the bauble to switch with his child self, creating a loop in which the real magic orb would have been destroyed had no time travel taken place.
*In ', the game starts with the character Princess Elise in possession of the blue Chaos Emerald. She later loses possession of it, and it is recovered by Silver the Hedgehog, who takes it into the past and gives it to a young Elise. The blue Emerald is therefore ontologically looped. Also in this game, Shadow the Hedgehog is attacked by Mephiles the Dark, who recognises him despite Shadow never having seen Mephiles before. Shadow's subsequent vengeful pursuit of Mephiles leads him to travel back in time (with Silver) and meet Mephiles in the past. Here it is Shadow and Mephiles' feud which apparently has no origin. Mephiles only attacked Shadow because Shadow attacked Mephiles in the past; but Shadow only travelled to the past because Mephiles attacked him in the present.Furthermore because Elise always had the emerald, most of the other games in the series could not have taken place as Sonic needs all seven emeralds to turn into his super form, to defeat the Final Boss. However, the ending of the game negates this paradox by preventing the entire game's events from ever having occurred.
*In Final Fantasy VIII, the main protagonist, Squall Leonhart, is a member of an elite fighting force, the SeeD, having been trained at an institution known as 'Garden'. SeeD's mission statement is a vague one, simply 'to defeat the sorceress.' As a result of time decompressing after 'defeating the sorceress', Squall arrives 17 years into his own past to meet the founder of Garden, Edea Kramer. He tells her that a sorceress from the distant future will try to compress all of existence into a singularity and reform it to her liking. At this time, the child Squall was under Edea's care, so she placed him into Garden to become a SeeD, where he was trained to one day kill the Sorceress Ultimecia. Since Squall was raised by the Garden, and he gave Edea the idea to create Garden, the concepts of Garden, SeeD, and 'defeating the sorceress' are of indeterminate origin.
*In Mario and Luigi: Partners in Time, Mario and Luigi are sent back in time to the point when they were babies. The four characters team up and work together through the game, going back and forth to past and present times. This makes a time loop, as, for example, since Baby Mario and Baby Luigi are, during the time the four work together, able to remember almost exactly what happens during that time. They both grow up, and the story begins again, this time with the present Mario and Luigi being what used to be their past selves. Remembering what happened, the present brothers can change what happened in the story, most likely to benefit themselves or their baby selves, creating a time loop. Another example of a time loop is if when the present Mario and Luigi are still working with Baby Mario and Baby Luigi, they are severely damaged from a battle. If the babies, say, broke their legs, they wouldn't be able to go through past games (assuming they are in time order), such as Super Mario Bros or, more importantly, this game. Yet another argument is, since it's during Baby Mario's time, it may interfere with the storyline of Yoshi's Island, again, creating a time loop.
*In World of Warcraft:
**The quest to gain entrance into the instance of Karazhan involves an ontologically looped key. Khadgar, who once was the apprentice to Medivh, sends the player out to collect the three pieces of the key to Karazhan, which he got from Medivh. After gathering all pieces, Khadgar sends the player back in time so that Medivh can empower the reassembled key to actually open Karazhan-Medivh however keeps the key that the player brought and says, that he will give the key to his apprentice Khadgar thereby closing the loop.
**The player character is given a quest by a time traveling character in which a future version of the player character joins the present version to fight tamperers in the timeline. Several levels later, the player must take the role of the future version of the player.
*In Shin Megami Tensei: Strange Journey, the Protagonist finds a group of Disir who beg him to travel to a determinate location and destroy Yggdrasil, who had been feeding upon their powers. Upon arrival, the Protagonist is easily defeated by Yggdrasil and left nearly for dead. While he's nearly unconscious, another person, much stronger than him, destroys Yggdrasil. The Disir thank him anyway and send him on his way. Much later in his personal timeline, the Protagonist finds the Norns, the empowered descendants of the Disir, who use their timetravelling powers to deposit him in the battle he almost lost to Yggdrasil in the past and finish him off without tipping off his former self, creating an endless cycle as he leaves.

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